CODEWITHSUNDEEP
c#wpfcollections
PeterP
PeterP

Reputation: 771

Find Item in ObservableCollection without using a loop

Currently i have the following syntax (list is a list containing objects with many different properties (where Title is one of them):

for (int i=0; i < list.Count; i++)
{
   if(title == list[i].Title)
   {
    //do something
   }
}

How can i access the list[i].Title without having to loop over my entire collection? Since my list tends to grow large this can impact the performance of my program.

I am having a lot of similar syntax across my program (accessing public properties trough a for loop and by index). But im a sure there must be a better and elegant way of doing this?

The find method does seem to be a option since my list contains objects.

Upvotes: 47

Views: 129025

Answers (10)

Jan
Jan

Reputation: 1

An observablecollection can be a List

{
    BuchungsSatz item = BuchungsListe.ToList.Find(x => x.BuchungsAuftragId == DGBuchungenAuftrag.CurrentItem.Id);
}

Upvotes: -2

mjordan
mjordan

Reputation: 369

Maybe this approach would solve the problem:

int result = obsCollection.IndexOf(title);

IndexOf(T)
Searches for the specified object and returns the zero-based index of the first occurrence within the entire Collection.

(Inherited from Collection)

https://learn.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.observablecollection-1?view=netframework-4.7.2#methods

Upvotes: -1

haxpak
haxpak

Reputation: 105

i had to use it for a condition add if you don't need the index

using System.Linq;

use

if(list.Any(x => x.Title == title){
// do something here
}

this will tell you if any variable satisfies your given condition.

Upvotes: 7

Tigran
Tigran

Reputation: 62256

I Don't know what do you mean exactly, but technially speaking, this is not possible without a loop.

May be you mean using a LINQ, like for example: 

list.Where(x=>x.Title == title)

It's worth mentioning that the iteration over is not skipped, but simply wrapped into the LINQ query.

Hope this helps.

EDIT

In other words if you really concerned about performance, keep coding the way you already doing. Otherwise choose LINQ for more concise and clear syntax.

Upvotes: 70

Dan Busha
Dan Busha

Reputation: 3803

You're looking for a hash based collection (like a Dictionary or Hashset) which the ObservableCollection is not. The best solution might be to derive from a hash based collection and implement INotifyCollectionChanged which will give you the same behavior as an ObservableCollection.

Upvotes: 2

Brian
Brian

Reputation: 4984

I'd suggest storing these in a Hashtable. You can then access an item in the collection using the key, it's a much more efficient lookup.

var myObjects = new Hashtable();
myObjects.Add(yourObject.Title, yourObject);
...
var myRetrievedObject = myObjects["TargetTitle"];

Upvotes: 5

memo
memo

Reputation: 441

Well if you have N objects and you need to get the Title of all of them you have to use a loop. If you only need the title and you really want to improve this, maybe you can make a separated array containing only the title, this would improve the performance. You need to define the amount of memory available and the amount of objects that you can handle before saying this can damage the performance, and in any case the solution would be changing the design of the program not the algorithm.

Upvotes: 0

Daren Thomas
Daren Thomas

Reputation: 70324

Consider creating an index. A dictionary can do the trick. If you need the list semantics, subclass and keep the index as a private member...

Upvotes: 4

Roberto
Roberto

Reputation: 524

ObservableCollection is a list so if you don't know the element position you have to look at each element until you find the expected one.

Possible optimization If your elements are sorted use a binary search to improve performances otherwise use a Dictionary as index.

Upvotes: 2

Patryk Ćwiek
Patryk Ćwiek

Reputation: 14328

Here comes Linq:

var listItem = list.Single(i => i.Title == title);

It throws an exception if there's no item matching the predicate. Alternatively, there's SingleOrDefault.

If you want a collection of items matching the title, there's:

var listItems = list.Where(i => i.Title ==  title);

Upvotes: 43

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